WO2008053238A2

WO2008053238A2 - System for charging and discharging containers for storage & transportation of high pressure compressed gas

Info

Publication number: WO2008053238A2
Application number: PCT/GB2007/004205
Authority: WO
Inventors: Donald Arthur Ferns; David John Loader
Original assignee: SNC-LAVALIN UK Ltd; SNC Lavalin UK Ltd
Current assignee: SNC-LAVALIN UK Ltd; Kent International Ltd
Priority date: 2006-11-02
Filing date: 2007-11-02
Publication date: 2008-05-08
Anticipated expiration: 2009-05-02
Also published as: WO2008053238A3; GB0621879D0

Abstract

A fluid tight container for storage and transportation of high pressure compressed gas, the container (110) having a first connection (112) which serves as an inlet and outlet for gas to be stored in the container, a flexible impermeable membrane (111) dividing the container into a first portion (115) for gas and communicating with the first connection, and a second portion (116) for liquid, in which the second portion communicates with a second connection (114) for introducing or withdrawing liquid from the second portion. The invention facilitates the charging and discharging of the gas at a controlled pressure.

Description

SYSTEM FOR CHARGING AND DISCHARGING CONTAINERS FOR STORAGE & TRANSPORTATION OF HIGH PRESSURE COMPRESSED GAS

Technical Field of the Invention

The invention relates to a system for charging and discharging containers for storage and transportation of high pressure compressed gas, and to a method of storing such gas within a container.

Background of the Invention

A common method of gas storage and transportation is at pressure within a container. Containers can vary in size from small portable gas cylinders for domestic purposes to large storage tanks for industrial use.

One example of a method of storing gas at low pressures is described in UK Patent Specification No. 2,399,052. This is concerned with the storage of oxygen at a pressure of less than 1 bara, and specifically at less than 0.5 bara. An outer shell surrounds a collapsible bladder containing oxygen. When needed for small scale domestic welding, oxygen is forced out of the bladder by pumping air into the space between the bladder and the shell. The disclosure is essentially of a low pressure system for domestic use.

Storage pressures can be many hundreds of atmospheres - the higher the pressure, the more gas is stored. In the field of transportation this method is being used or proposed for ships, freight trains, river and canal barges, and road trucks. This invention is applicable to gas storage pressures of about 50 bara or greater, and references to high pressure compressed gas imply pressures of this order or greater.

The process of charging and discharging of containers for these high pressure systems has several drawbacks as follows:

1. The time taken to empty a container is controlled by the rate of transfer which is primarily governed by the internal pressure in the container. To recover even 90% of the gas can take a protracted time.

2. The normal process of gas expansion or compression results in a change in temperature resulting in cooling or heating of the container, pipe- work system and surroundings. For large systems this can require the provision of extensive HVAC facilities to stabilize the temperature.

3. As the pressure in the system decreases, a compressor is required to bring the gas up to delivery pressure.

4. At a certain point depending on the composition of the gas, the pressure and temperature changes can result in the formation of liquids in the gas. 5. The rise in temperature during charging decreases the amount of gas that can be stored at a given pressure. In applications such as road transport running on Compressed Natural Gas (CNG) this reduces the amount of fuel that can be stored and reduces the vehicle range. 6. The low temperature at the end of discharging can restrict the amount of gas taken out.

7. The low temperature during discharge can require the use of special materials for the construction of the container and associated pipe work system.

Disclosure of the Invention

The invention provides a fluid tight container for storage and transportation of high pressure compressed gas, the container having a first connection which serves as an inlet and outlet for gas to be stored in the container, a flexible impermeable membrane dividing the container into a first portion for gas and communicating with the first connection, and a second portion for liquid, in which the second portion communicates with a second connection for introducing or withdrawing liquid from the second portion. In one form it is preferred that the membrane is in the form of a bladder within the container, and the second portion is within the bladder.

It is further preferred that the bladder hangs down from the top of the container.

Alternatively, the bladder is disposed across a part of the container intermediate between the top and the bottom of the container, and is inflatable upwardly and downwardly by liquid to displace the gas.

In another preferred form, the second portion is outwith the bladder, so that gas may be contained within the bladder.

In yet another preferred form, the membrane extends across the interior of the container.

In this last mentioned form, it is preferred that the membrane is secured to the internal periphery of the container intermediate between the top and the bottom of the container, and the first and second connections are on opposite sides of the membrane. Alternatively, the membrane extends from top to bottom of the container, and the first and second connections are on each side of the membrane.

Alternatively, the membrane extends across the container generally horizontally, and the first and second connections are above and below the membrane. There may be a plurality of first connections and/or a plurality of second connections.

In another preferred form there are a plurality of compartments separated by multiple membranes.

In yet another preferred form, the pressure on one side (the liquid side) of the membrane is from a hydraulic or mechanical piston. The invention includes a container as described above, in combination with means to pump liquid into and out of the second portion, and so to control the volume of liquid within the second portion.

The invention also includes a method of discharging gas from a fluid tight container for the storage and transportation of high pressure compressed gas which comprises the steps of: a) Constraining gas in a first portion of the container on one side of a flexible impermeable membrane, and in communication with a first connection which serves as an inlet and outlet for gas to be stored within the container; b) pumping liquid into a second portion of the container on the other side of the membrane so that the gas on the one side of the flexible membrane is maintained at a constant pressure; and c) discharging gas from the first portion of the container.

The steps of the method described above may be performed in the reverse order, using the same techniques for the maintenance of constant pressure.

The invention permits a method of maintaining pressure during the charging and discharging of gas containers, so overcoming many of the drawbacks listed by number in the section entitled 'Background to the Invention'. The following description focuses on discharging but the invention is equally applicable to charging.

This device and methodology applies to any gas container. The proposed method is to install a flexible membrane inside the container. The membrane separates the gas from a suitable liquid. (In hydrocarbon gas applications, diesel would be one such liquid). The membrane can be in the form of a diaphragm or bladder or a multiplicity of diaphragms or bladders within the gas container. A control and pump system maintains the pressure of the liquid equal to that of the gas. When the container is empty the flexible membrane sags to the bottom of the container or hangs from a support under its own weight. When gas is introduced and pressurized to the containment pressure, the membrane is compressed against one end or wall of the container or remains hanging in the container. Alternatively the liquid can be used to pressurize the container and the charging be carried out at constant or controlled pressure.

Gas can be introduced at one or more locations to charge the container as long as they are all on one side of the membrane. When the gas is to be discharged, liquid is introduced to the other side of the membrane and pressurized to the same pressure as the gas. The liquid is relatively incompressible and of a much higher density compared to the gas. Therefore it can be transferred into the container and pressurized quickly without significant change in temperature. The liquid is continually pumped in to maintain the pressure as the gas is transferred out from the other side of the membrane. This enables the container to be discharged at a constant pressure minimizing the temperature change of the gas, container and piping system. It also maximizes the amount of gas that can be exhausted from the container. The liquid is reusable and is emptied utilizing the small amount of pressurized gas remaining in the system after discharge and/or using a suitable pump. At any given time the pressure across the membrane is limited to ensure integrity of the flexible membrane is maintained. The discharge can consist of multiple phases of variable and constant pressure to optimize the fluid pump rating. For some hydrocarbon gases as the pressure drops the density reduces at a variable rate. At the higher pressures it can drop slowly and then below certain values it drops more rapidly. Therefore there is an optimum combination of venting down to a given pressure and then using the liquid via the bladder/membrane to discharge at constant pressure.

An alternative variation is a diaphragm maintaining the pressure in two halves of the container and allowing two simultaneous discharge locations.

A further alternative variation is to compartmentalize the container further and introduce more complex bladders/membranes and further additional outlets. A further option is to use a piston instead of the liquid to provide the pressure on one side of the membrane.

Brief Description of the Drawings

Several specific embodiments of the invention will now be illustrated by way of example with reference to the accompanying drawings, in which :- Figures 1 to 3 show a container having an inflatable hanging bladder;

Figure 4 shows a container having an inflatable transverse bladder;

Figures 5 and 6 show a container having a single tranverse membrane;

Figure 7 is a side elevation, showing the installation of containers in a ship; and

Figure 8 is a plan view looking down from above on the installation of Fig 7. Description of specific embodiments of the Invention

Figures 1 to 6 illustrate diagrammatically typical storage containers for compressed natural gas. Figure 1 shows the container 10 filled with gas and with an un-infϊated bladder 11 suspended from the upper nozzle 12. The bladder 11 can be pressurized with liquid through nozzle 12 in order to facilitate discharge of gas through a lower nozzle 14, while controlling the pressure in the container.

The lower nozzle 14 is regarded as a first connection, and the upper nozzle 12 is regarded as a second connection. The bladder 11 is formed of a flexible impermeable membrane separating first and second portions 15 and 16 for gas and liquid respectively. A partially discharged container 10 is illustrated in figure 2. At this point liquid balancing the pressure of the gas within the container is introduced through the upper nozzle 12 and inflates the bladder 11. The discharging process continues until substantially all the gas is discharged through the lower nozzle 14, and the bladder is fully inflated (as illustrated in fig. 3).

There are wide ranges of configurations of the membrane separating the gas and liquid. Figure 4 illustrates a central horizontal bladder 17 with two gas compartments 18 and 19. In this case there are upper and lower gas inlet/outlets 21a and 21b, and peripheral bladder charging ports 22a and 22b. If turned through 90deg, the bladder 17 would be central and vertical, the gas inlet/outlets would be at the sides, and the liquid charging ports would be at the top and bottom. Figures 5 and 6 illustrate a central membrane system empty and half full. In this case a single flexible membrane 23 extends across the interior of the container 10. Upper nozzle 24 is available for gas to enter or leave first portion 26, and lower nozzle 25 is available for liquid to be pumped out of/into second portion 27 of the container 10 to admit or expel gas. A typical application of this would be in the containers within a CNG transport ship. These are frequently a series of separate containers usually of proprietary design. Each container would be fitted with a membrane and a liquid control system used to control discharge and possibly charging of the containers.

Figures 7 and 8 illustrate a typical application in a palletized array of bottles. There are a number of proprietary bottle designs available made of a variety of materials including steel and GRP. The bottles are set in supporting frames within the hold of transport vessels or barges. Smaller versions can be used on road and rail transport.

The figures illustrate a 4 by 4 array of bottles 110 in a frame. A flexible impermiable membrane 111 is shown attached to an upper inlet 112 for gas. The membrane is shown at various typical stages of inflation from left to right as gas is charged into the container. Discharge of gas would be effected as shown from right to left. The gas is charged and discharged through a manifold (112) at the top, and liquid is introduced and extracted from the bottom through a lower inlet 114. The first portion (occupied by gas) is designated 115, and the second portion (occupied by liquid) is designated 116.

Typical pressures are likely to be between 100 and 300 bara, but could go higher or lower.

The liquid used in this process is stored in a tank at a quayside or depot along with the associated pump. In the ship/barge application illustrated it is used for discharge at a quay. Sufficient liquid is required to enable a group of bottles to be discharged simultaneously. The liquid is then removed and used in the next array until the entire ship is discharged. A further application would be in the storage tanks on CNG powered motor vehicles. The membrane would be fitted in the tank and during refueling the liquid would be introduced first and the tanks filled at constant pressure. This would allow more gas to be injected into the tank and provide a higher range to the vehicle. Advantages of the Invention

The advantages of embodiments described above are:

1. Control of the pressure of the gas during all phases of the discharge.

2. Eliminates mingling of displacing liquid with the stored gas.

3. Eliminates the need for heating/cooling systems to compensate for temperature changes.

4. Reduces the discharge time.

5. Eliminates the need for a discharge compressor system.

6. Provides a means of avoiding phase changes (liquid formation or hydrates) in the gas. 7. Increases the amount of gas discharged.

8. Maximizes the gas intake of a container by maintainer the charging pressure and minimizing the temperature increase.

Claims

1/ Fluid tight container for storage and transportation of high pressure compressed gas, the container having a first connection which serves as an inlet and outlet for gas to be stored in the container, a flexible impermeable membrane dividing the container into a first portion for gas and communicating with the first connection, and a second portion for liquid, in which the second portion communicates with a second connection for introducing or withdrawing liquid from the second portion.

2/ A container as claimed in claim 1, in which the membrane is in the form of a bladder within the container, and the second portion is within the bladder.

3/ A container as claimed in claim 2, in which the bladder hangs down from the top of the container.

4/ A container as claimed in claim 2, in which the bladder is disposed across a part of the container intermediate between the top and the bottom of the container, and is inflatable upwardly and downwardly by liquid to displace the gas.

5/ A container as claimed in any one of claims 2 to 4, in which the second portion is out with the bladder, so that gas may be contained within the bladder.

6/ A container as claimed in claim 1, in which the membrane extends across the interior of the container.

11 A container as claimed in claim 6, in which the membrane is secured to the internal periphery of the container intermediate between the top and the bottom of the container, and the first and second connections are on opposite sides of the membrane.

8/ A container as claimed in claim 6, in which the membrane extends from top to bottom of the container, and the first and second connections are on each side of the membrane.

91 A container as claimed in claims 6, in which the membrane extends across the container generally horizontally, and the first and second connections are above and below the membrane.

10/ A container as claimed in any one of the preceding claims, in which there are a plurality of first connections. 11/ A container as claimed in any one of claims 1 to 9, in which there are a plurality of second connections.

12/ A container as claimed in any one of claims 1 to 9, in which there are a plurality of both first and second connections.

13/ A container as claimed in any one of the preceding claims, in which there are a plurality of compartments separated by multiple membranes.

14/ A container as claimed in any one of the preceding claims, in which the pressure on one side (the non gas side) of the membrane is a hydraulic or mechanical piston.

15/ A container as claimed in any one of the preceding claims in combination with means to pump liquid into and out of the second portion, and so to control the volume of liquid within the second portion.

16/ A method of discharging gas from a fluid tight container for the storage and transportation of high pressure compressed gas which comprises the steps of: a) Constraining gas in a first portion of the container on one side of a flexible impermeable membrane, and in communication with a first connection which serves as an inlet and outlet for gas to be stored within the container; b) pumping liquid into a second portion of the container on the other side of the membrane so that the gas on the one side of the flexible membrane is maintained at a constant pressure; and c) discharging gas from the first portion of the container.

17/ A method of charging a container, comprising the steps of claim 16 performed in the reverse order, using the same techniques for the maintenance of constant pressure.

18/ A container substantially as hereinbefore described by way of example with reference to and as shown in the accompanying drawings.

19/ A method substantially as hereinbefore described by way of example with reference to the accompanying drawings.